Optical fiber cable

ABSTRACT

An optical fiber cable includes a core that includes optical fibers, a sheath that accommodates the core, and an interposed layer disposed between the core and the sheath. The interposed layer includes sheet materials arranged in a circumferential direction of the optical fiber to cover the core. Each of the sheet materials includes fibers solidified by a matrix.

TECHNICAL FIELD

The present invention relates to an optical fiber cable.

BACKGROUND

Japanese Unexamined Patent Application, First Publication No.2013-228647 discloses an optical fiber cable provided with a bufferlayer on the outer periphery of a core in which a plurality of opticalfibers are bundled in order to reliably protect the internal opticalfibers from external force or the like. The buffer layer is wound aroundthe outer periphery of the core of the optical fiber such that the edgesof the tape-shaped member are in contact with each other. A holdingbinder is wound around the outer periphery of the tape-shaped member tofix the tape-shaped member wound in a cylindrical shape.

Incidentally, in such an optical fiber cable, when accessing to theoptical fiber inside the buffer layer in the mid-span access operationor the like, an operation of cutting the holding binder, spreading thetape-shaped member, and accessing to the optical fiber is required.Therefore, the operation time of the mid-span access operation may beincreased.

As described above, this type of optical fiber cable is required to havea configuration for protecting an optical fiber, and be able to easilyaccess to an optical fiber disposed inside of the optical fiber cable.

SUMMARY

Embodiments of the present invention provide an optical fiber cablecapable of easily accessing to an internal optical fiber while having aconfiguration for protecting the optical fiber.

An optical fiber cable according to one or more embodiments of thepresent invention includes a core having a plurality of optical fibers;a sheath that accommodates the core; and an interposed layer disposedbetween the core and the sheath, in which the interposed layer has aplurality of sheet materials arranged in a circumferential direction soas to cover the core, and each of the plurality of sheet materialsincludes fibers solidified by a matrix.

According to one or more embodiments of the present invention, it ispossible to provide an optical fiber cable which has a configuration forprotecting an optical fiber, and can easily access to an optical fiberdisposed inside of the optical fiber cable.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 1B is an enlarged view showing an example of the structure of asheet material of FIG. 1A.

FIG. 1C is a transverse cross-sectional view of the optical fiber cableof FIG. 1A after the sheath has been torn along a longitudinaldirection.

FIG. 1D is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 2A is a view showing a method for manufacturing the optical fibercable according to one or more embodiments.

FIG. 2B is a view showing a step following FIG. 2A.

FIG. 2C is a view showing a step following FIG. 2B.

FIG. 2D is a view showing a step following FIG. 2C.

FIG. 3A is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 3B is a transverse cross-sectional view of the optical fiber cableof FIG. 3A after the sheath has been torn along a longitudinaldirection.

FIG. 4A is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 4B is a schematic view of an interface between a sheath and a sheetmaterial of the optical fiber cable of FIG. 4A.

FIG. 4C is a transverse cross-sectional view of the optical fiber cableof FIG. 4A after the sheath has been torn along a longitudinaldirection.

FIG. 5A is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 5B is a schematic view showing a step of fixing a plurality ofsheet materials to each other, in a manufacturing step of the opticalfiber cable according to one or more embodiments.

FIG. 6 is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

FIG. 7 is a transverse cross-sectional view showing the structure of anoptical fiber cable according to one or more embodiments.

DETAILED DESCRIPTION

The configuration of an optical fiber cable according to one or moreembodiments will be described below with reference to FIG. 1A.

As shown in FIG. 1A, an optical fiber cable 10A of one or moreembodiments includes a core 8 having a plurality of optical fibers 1 a,an interposed layer 4, a sheath 5 provided outside the interposed layer4, and a pair of ripcords 7 embedded in the sheath 5.

Here, in one or more embodiments, the sheath 5 is formed in acylindrical shape having a common central axis O.

In one or more embodiments, a direction along the central axis O iscalled a longitudinal direction, and a cross section orthogonal to thelongitudinal direction is called a transverse cross section. Further, inthe transverse cross-sectional view, a direction intersecting thecentral axis O is referred to as a radial direction, and a directionrevolving around the central axis O is referred to as a circumferentialdirection. The case where the optical fiber cable 10A or its constituentmembers are viewed from the outside in the radial direction is calledside view.

The core 8 includes a plurality of optical fiber units 1 each having aplurality of optical fibers 1 a, and a wrapping tube 2 wrapping theseoptical fiber units 1. The plurality of optical fiber units 1 aretwisted in an SZ shape or a spiral shape, and wrapped by the wrappingtube 2. In addition, the core 8 may be configured by wrapping oneoptical fiber unit 1 with the wrapping tube 2.

As the wrapping tube 2, a nonwoven fabric, a polyester tape, or the likecan be used. Further, as the wrapping tube 2, a water-absorbing tapeobtained by imparting water-absorbing property to a nonwoven fabric, apolyester tape, or the like may be used. In this case, the waterproofperformance of the optical fiber cable 10A can be improved. It should benoted that the core 8 may not be provided with the wrapping tube 2.However, when the wrapping tube 2 is provided, since the optical fiberunit 1 is wrapped by the wrapping tube 2, the optical fiber 1 a can bemore protected from external force.

The optical fiber unit 1 of one or more embodiments includes a pluralityof optical fibers 1 a and a binding material 1 b that bundles theoptical fibers 1 a. As the optical fiber 1 a, an optical fiber corewire, an optical fiber strand, an optical fiber ribbon, or the like canbe used. As one type of optical fiber ribbon, the plurality of opticalfibers 1 a may form a so-called intermittently-fixed ribbon. In theintermittently-fixed ribbon, when the plurality of optical fibers 1 aare pulled in a direction orthogonal to the extending direction thereof,the optical fibers are adhered to each other so as to spread in a meshshape (spider web shape). Specifically, one optical fiber 1 a is adheredto adjacent optical fibers 1 a on both sides thereof at differentpositions in the longitudinal direction, and the adjacent optical fibersla are adhered to each other at a fixed interval in the longitudinaldirection.

In addition, the aspect of the optical fiber 1 a included in the core 8is not limited to the intermittently-fixed ribbon, and may beappropriately changed.

The binding material 1 b may be in a string shape, a sheet shape, or atube shape. Further, the plurality of optical fibers 1 a may be wrappedby the wrapping tube 2 without being bundled (that is, withoutconstituting the optical fiber unit 1).

Alternatively, the plurality of optical fibers 1 a may be bundled bybeing twisted together to form the optical fiber unit 1. In this case,the optical fiber unit 1 may not have the binding material 1 b.

In FIG. 1A and the like, the cross-sectional shape of the optical fiberunit 1 is arranged, but the cross-sectional shape may collapse due tothe movement of the optical fiber 1 a in the optical fiber unit 1. InFIG. 1A and the like, three optical fiber units 1 form an inner layer,and seven optical fiber units 1 form an outer layer. However, a part ofthe outer layer may enter the inner layer. Alternatively, the opticalfiber units 1 may not form these layers.

Further, in FIG. 1A and the like, the plurality of optical fiber units 1are arranged with uniform gaps, but there may be no gaps or the gaps maybe uneven. Alternatively, a filling may be inserted between the opticalfiber units 1 so as to adjust the installing density of the opticalfibers 1 a on the core 8 and arrange the shape of the core 8.

The interposed layer 4 is located between the core 8 and the sheath 5and has a plurality of sheet materials 3. The plurality of sheetmaterials 3 extend linearly along the longitudinal direction, and aredisposed so as to cover the entire circumference of the core 8. Theinterposed layer 4 of one or more embodiments has a single-layerstructure in which each of the plurality of sheet materials 3 isdisposed so as to be at least partially in contact with the core 8. The“single-layer structure” includes a case where the sheet materials 3 donot overlap in the radial direction as shown in FIG. 1A. In addition,the “single-layer structure” includes the other case where, for example,only end parts of some or all of the sheet materials 3 in thecircumferential direction overlap in the radial direction as shown inFIG. 1D.

As shown in FIG. 1A, each sheet material 3 is curved in an arc shapealong a curved surface on the outer periphery of the core 8. In theexample shown in FIG. 1A, the end parts of the sheet materials 3 in thecircumferential direction are in contact with each other, and the entirecircumference of the core 8 is covered with the eight sheet materials 3.For example, in an optical fiber cable having 288 optical fibers 1 a,eight sheet materials 3 having a thickness of 0.4 to 0.5 mm in a radialdirection and a width of 3.5 mm in a circumferential direction are used.The number and dimensions of the sheet material 3 used for the opticalfiber cable 10A are not limited to this example, and may beappropriately changed according to the outer diameter of the core 8 andthe characteristics required for the interposed layer 4.

The ripcord 7 is a thread of a synthetic fiber such as polyester or thelike, and is used to tear the sheath 5. Further, as the ripcord 7, acylindrical rod made of polypropylene (PP) or nylon may be used. Thepair of ripcords 7 are disposed so as to sandwich the core 8therebetween in the radial direction. The number of the ripcords 7embedded in the sheath 5 may be one or three or more.

In the example shown in FIG. 1A, each ripcord 7 is disposed radiallyoutside one sheet material 3. Not limited to this example, each ripcord7 may be disposed so as to contact two sheet materials 3.

The sheath 5 covers the core 8, the plurality of sheet materials 3, andthe ripcord 7. As the material of the sheath 5, polyolefin (PO) resinssuch as polyethylene (PE), polypropylene (PP), ethylene ethyl acrylatecopolymer (EEA), ethylene vinyl acetate copolymer (EVA), and ethylenepropylene copolymer (EP), polyvinyl chloride (PVC), or the like can beused. Further, a mixture (alloy, mixture) of the above resins may beused.

A mark for indicating the position of the ripcord 7 may be provided onthe outer peripheral surface of the sheath 5. The mark may be a markingmade of paint, a protrusion protruding radially outward, or a grooverecessed radially inward. These marks may extend along the longitudinaldirection.

Note that the material forming the sheath 5 may include capsaicin andthe like. In this case, it is possible to prevent an animal such as arat from biting the sheath 5.

<Configuration of Sheet Material 3>

The sheet material 3 includes, for example, as shown in FIG. 1B, fibers3 a solidified by a matrix 3 b. As the fiber 3 a used for the sheetmaterial 3, glass fiber, aramid fiber, carbon fiber, metal fiber (forexample, iron fiber, stainless steel fiber) or the like can be used.Since these fibers 3 a have high tensile strength, the fibers 3 a aresuitable when the sheet material 3 is used as a tension member. As thematrix 3 b for fixing the fibers 3 a, a thermosetting resin such as anepoxy resin, a thermoplastic resin, an ultraviolet curable resin, anelastomer (rubber), or the like can be used. The sheet material 3 may bea so-called fiber reinforced plastic (FRP).

The type of the fiber 3 a can be selected according to thecharacteristics required for the optical fiber cable 10A.

For example, since glass fiber has an insulating property, aconfiguration for grounding is not required. Further, the unit price islower than that of aramid fiber. On the other hand, compared to othermaterials (fibers), the tensile strength is lower. Further, since theamount of contraction of the glass fiber at a low temperature is small,the contraction of the sheet material 3 in a low-temperature environmentcan be reduced. Therefore, the stress applied to the optical fiber 1 adue to the contraction of the sheet material 3 can be reduced.

Since the aramid fiber has an insulating property, a configuration forgrounding is not required. It also has higher tensile strength comparedto glass fibers. On the other hand, for example, when the sheath 5 tendsto contract in a low temperature environment, the ability of the aramidfiber to suppress the contraction deformation is relatively low, and theoptical fiber 1 a is likely to be affected. Further, the unit price ishigher than that of glass fiber.

Since carbon fibers have high tensile strength, the carbon fibers aremore suitable when the sheet material 3 is used as a tension member. Onthe other hand, since the unit price is high and has conductivity, aconfiguration for grounding the sheet material 3 may be required.

To form the sheet material 3, the fibers 3 a are soaked in the matrix 3b while keeping the directionality (orientation) of the fibers 3 a, andthen the matrix 3 b is cured. In this case, the sheet material 3 becomesresistant to tension in the extending direction of the fibers 3 a (fiberdirection). By disposing the sheet material 3 such that the fiberdirection of the sheet material 3 coincides with the longitudinaldirection of the optical fiber cable 10A, the sheet material 3 can beused as a tension member of the optical fiber cable 10A. The tensilestrength of the sheet material 3 can be adjusted, for example, bychanging the type and amount of the fibers 3 a of the sheet material 3and changing the cross-sectional area of the sheet material 3.

In an optical fiber cable in the related art, for example, a metal wire(such as a steel wire) or an FRP rod is used as a tension member, andthese tension members are embedded in a sheath covering a core. On theother hand, the optical fiber cable 10A of one or more embodiments shownin FIG. 1A uses a plurality of sheet materials 3 formed of fiberreinforced plastic as a tension member, and therefore does not include atension member other than the plurality of sheet materials 3.

Accordingly, even when the optical fiber cable 10A does not include atension member other than the sheet material 3, the optical fiber 1 acan be protected from tension when the optical fiber cable 10A is pulledin the longitudinal direction. Further, since there is no need todispose a tension member other than the sheet material 3, the weight anddiameter of the optical fiber cable 10A can be reduced. Furthermore, incross-sectional view, since the sheet material 3 which is a tensionmember is uniformly disposed over the entire circumference of theoptical fiber cable 10A, the flexibility of the optical fiber cable 10Ais not directional and is easily bent in any direction. Therefore,workability at the time of installing the optical fiber cable 10A can beimproved.

The optical fiber cable 10A may include a tension member other than theplurality of sheet materials 3. Further, the sheet material 3 may be aresin obtained by fixing a fiber layer in which fibers 3 a are woven bya matrix 3 b.

Further, the sheet material 3 has high strength against an externalforce to tear along the direction orthogonal to the fiber direction.Therefore, the optical fiber la can be protected from external force bythe sheet material 3.

For example, optical fiber cables that are built, laid, or buried in amountain or a forest may be bitten by wild animals such as mice,squirrels, and woodpeckers (biting injury), so an optical fiber insidethe cable may be damaged. In the optical fiber cable 10A of one or moreembodiments, the end parts in the radial direction of the sheetmaterials 3 are in contact with each other, and the core 8 is coveredwith the sheet materials 3 without any gaps. Thereby, the optical fiberla can be reliably protected from biting injury.

<Method of Taking Out Core 8 from Optical Fiber Cable 10A>

First, using a tool such as an electric knife, a part of the sheath 5 isstripped off to expose a part of the ripcord 7. The exposed ripcord 7 ispulled in the direction of the arrow shown in FIG. 1A, and the sheath 5is torn along the longitudinal direction. Thereby, as shown in FIG. 1C,the sheath 5 is divided into two parts in the circumferential direction,and the sheet materials 3 are separated from the outer periphery of thecore 8, so that the core 8 can be taken out.

In the access operation of the optical fiber cable 10A, an operation oftaking out the core 8 from the optical fiber cable 10A, and accessing tothe target optical fiber from the inside of the core 8 is performed. Inorder to perform the access operation more smoothly, it is necessary toreduce the labor for removing the sheath 5 and the sheet material 3disposed outside the core 8.

Compared with an optical fiber cable in the related art having a bufferlayer and a holding binder wound around a core, the optical fiber cable10A of one or more embodiments does not require an operation of removingthe wound buffer layer and the holding binder. Therefore, the accessoperation of the optical fiber cable 10A can be performed more smoothly.

(Method for Manufacturing Optical Fiber Cable)

The optical fiber cable according to one or more embodiments can bemanufactured by a manufacturing method as shown in FIGS. 2A to 2D, forexample.

First, as shown in FIG. 2A, a plurality of optical fibers 1 a enter intoa cylindrical pipe P (entry step). As the pipe P, a material having ahigher melting point than the sheet material 3 and the sheath 5 andhaving high heat resistance can be suitably used. The shape of the pipeP may be cylindrical, square tubular, elliptical tubular, or the like.The optical fibers la that enter the pipe P may be in a state of beingbundled by the binding material 1 b, or may be in a state of beingwrapped by the wrapping tube 2. That is, in the entry step, theplurality of optical fibers 1 a in the state of the optical fiber unit 1or the core 8 may be entered into the pipe P.

Next, as shown in FIG. 2B, a plurality of sheet materials 3 to be theinterposed layer 4 are disposed around the pipe P in the circumferentialdirection so as to surround the optical fibers la (arrangement step).Thereby, the cylindrical interposed layer 4 having the same shape as thepipe P is formed. At this time, the sheet material 3 may be disposedsuch that the fiber direction in which the fiber 3 a extends areparallel with the longitudinal direction in which the optical fiber 1 aextends.

Next, the plurality of optical fibers 1 a pass through the pipe P whilebeing surrounded by the interposed layer 4 (passing step). At this time,the plurality of sheet materials 3 are moved on the outer peripheralsurface of the pipe P in accordance with the speed (linear speed) atwhich the optical fiber 1 a passes through the pipe P. This results in astate as shown in FIG. 2C.

Next, as shown in FIG. 2D, a sheath 5 that covers the interposed layer 4is formed (covering step). For example, the sheath 5 is formed aroundthe interposed layer 4 by extrusion molding. Thereby, the optical fibercable 10A is obtained.

According to the above-described manufacturing method, the interposedlayer 4 in which the plurality of sheet materials 3 are disposed in thecircumferential direction so as to surround the core 8 can be formedstably.

The method of manufacturing the optical fiber cable 10A is not limitedto the above. For example, a plurality of sheet materials 3 which arethe interposed layers 4 may be directly disposed around the core 8without using the pipe P.

As described above, the optical fiber cable 10A according to one or moreembodiments includes a core 8 having a plurality of optical fibers 1 a,a sheath 5 accommodating the core 8, and an interposed layer 4 disposedbetween the core 8 and the sheath 5. The interposed layer 4 includes aplurality of sheet materials 3 arranged in a circumferential directionso as to cover the core 8, and each of the plurality of sheet materials3 includes fibers 3 a solidified by a matrix 3 b.

According to the optical fiber cable 10A according to one or moreembodiments, since the plurality of sheet materials 3 have high strengthagainst external force, the optical fiber 1 a can be protected fromexternal force.

Further, during the taking-out-operation of the core 8, when the sheath5 is removed, each sheet material 3 is separated from the outerperiphery of the core 8, so that the operation of taking out the core 8can be performed smoothly.

Furthermore, if the sheet material 3 is used as a tension member, thereis no need to dispose a tension member other than the sheet material 3,so that the weight and diameter of the optical fiber cable 10A can bereduced. In addition, since the plurality of sheet materials 3 servingas tension members are disposed so as to cover the core 8, the opticalfiber cable 10A can be easily bent in any direction, and workabilitywhen installing the optical fiber cable 10A can be further improved.

Further, since the interposed layer 4 has a single-layer structure inwhich each of the plurality of sheet materials 3 is at least partiallyin contact with the core 8, the diameter of the optical fiber cable 10Acan be further reduced.

Further, in at least a part of adjacent sheet materials 3 among theplurality of sheet materials 3, end parts of the adjacent sheetmaterials 3 in the circumferential direction may abut each other. Sincethe core 8 is covered with the sheet material 3 without any gaps, theoptical fiber 1 a can be more reliably protected from external force.

Further, the sheet material 3 may extend linearly along the longitudinaldirection. With this configuration, when the sheath 5 is removed duringthe taking-out-operation of the core 8, the plurality of sheet materials3 are separated from the outer periphery of the core 8, so that theaccess operation of the optical fiber cable 10A can be performed moresmoothly.

Next, other embodiments of the present invention will be described, butthe basic configuration is the same as that of the above-describedembodiments. Therefore, the same reference numerals are given to similarconfigurations, the explanation thereof will be omitted, and onlydifferences will be described.

FIG. 3A shows an optical fiber cable 10B according to one or moreembodiments.

The optical fiber cable 10B of FIG. 3A is different from the opticalfiber cable 10A of FIG. 1A in that the ripcord 7 is fixed to at leastone of the plurality of sheet materials 3. In the example of FIG. 3A,two ripcords 7 are fixed to radially outer side surfaces of the twosheet materials 3, respectively. The ripcord 7 is not fixed to the othersix sheet materials 3. In order to fix the ripcord 7 to the sheetmaterial 3, for example, the matrix 3 b of the sheet material 3 may bemelted and the ripcord 7 may be fused. The ripcord 7 may be adhered tothe sheet material 3 with an adhesive applied to the outer periphery ofthe ripcord 7, or may be fixed by burying a part of the ripcord 7 in thesheet material 3.

In the optical fiber cable 10B, when the sheath 5 is torn along thelongitudinal direction by the ripcord 7, the sheet material 3 fixed tothe ripcord 7 can be removed together with the ripcord 7 as shown inFIG. 3B.

As described above, in the operation of taking out the core 8, the laborfor removing the sheet material 3 can be further reduced. Thereby, thetaking-out-operation of the core 8 can be performed more smoothly.

Further, when the ripcord 7 is pulled to tear the sheath 5, it ispossible to prevent a phenomenon that the ripcord 7 is not fixed in thesheath 5 and is pulled out (or come out) from the cable.

Next, other embodiments of the present invention will be described, butthe basic configuration is the same as that of the above-describedembodiments. Therefore, the same reference numerals are given to similarconfigurations, the explanation thereof will be omitted, and onlydifferences will be described.

FIG. 4A shows an optical fiber cable 10C according to one or moreembodiments.

The optical fiber cable 10C of FIG. 4A is different from the opticalfiber cable 10A of FIG. 1A in that the radially outer side surfaces ofthe plurality of sheet materials 3 are fixed to the sheath 5. Theripcord 7 covers the boundary between the sheet materials 3 adjacent toeach other in the circumferential direction from the radially outside.The plurality of sheet materials 3 and the sheath 5 may be fixed bypermeating a part of the sheet material 3 with a constituent material(resin or the like) of the sheath 5 as shown in FIG. 4B, for example. Inthis case, the constituent material of the sheath 5 enters between thefibers 3 a near the surface of the sheet material 3, and the fibers 3 aare buried in the matrix 3 b in other portions. Alternatively, thematrix 3 b of the sheet material 3 may be melted and fused to the sheath5. In this case, at the boundary between the sheet material 3 and thesheath 5, the constituent materials of the matrix 3 b and the sheath 5may be mixed.

In the optical fiber cable 10C, since the plurality of sheet materials 3are fixed to the sheath 5, when the sheath 5 is torn along thelongitudinal direction by the ripcord 7, as shown in FIG. 4C, the sheath5 and the plurality of sheet materials 3 fixed to the sheath 5 can beremoved.

As described above, the labor for removing the sheet material 3 at thetime of the taking-out-operation of the core 8 can be further reduced.Thereby, the taking-out-operation of the core 8 can be performed moresmoothly.

Further, since the plurality of sheet materials 3 which are the tensionmembers are fixed to the sheath 5, for example, contraction andexpansion in the longitudinal direction of the sheath 5 when thetemperature changes can be suppressed. Further, when the optical fibercable 10C is pulled in the longitudinal direction, it is possible toprevent the sheath 5 from being excessively elongated. Thereby, it ispossible to prevent a micro bending or tensile strain from being appliedto the optical fiber 1 a disposed inside the sheath 5.

Next, other embodiments of the present invention will be described, butthe basic configuration is the same as that of the above-describedembodiments. Therefore, the same reference numerals are given to similarconfigurations, an explanation thereof will be omitted, and onlydifferences will be described.

FIG. 5A shows an optical fiber cable 10D according to one or moreembodiments.

The optical fiber cable 10D of FIG. 5A is different from the opticalfiber cable 10A of FIG. 1A in that a plurality of sheet materials 3 arefixed to each other. The plurality of sheet materials 3 are adhered toeach other with an adhesive 6, for example, as shown in FIG. 5A. Theadhesive 6 is, for example, a thermosetting resin. In the example ofFIG. 5A, the adhesive 6 covers the entire outer peripheral surface ofthe interposed layer 4.

As a method for manufacturing the optical fiber cable 10D of one or moreembodiments, for example, after the arrangement step described in theabove-described embodiments, as shown in FIG. 5B, the sheet material 3may be heated by a heating device 9, and the matrices 3 b on thesurfaces of the sheet materials 3 may be melted and fused together(heating step). Alternatively, after the arrangement step described inthe above embodiments, an adhesive 6 made of a thermosetting resin maybe applied, and the adhesive 6 may be cured by heating.

The heating device 9 shown in FIG. 5B may be any device that can heat atleast the surface of the sheet material 3. As a specific example of theheating device 9, a heated metal die, a heating furnace, or the like canbe employed in addition to a rod-shaped heater as shown in FIG. 5B. Whenthe temperature at the time of extrusion molding of the sheath 5 ishigher than the melting point of the matrix 3 b, the matrices 3 b of thesheet materials 3 may be melted and fused to each other by heat at thetime when the sheath 5 is extruded to the outer periphery of theinterposed layer 4 and molded. In this case, the heating step and thecovering step can be performed simultaneously.

In one or more embodiments, since the plurality of sheet materials 3 arefixed to each other, the core 8 can be more reliably covered with thesheet materials 3 without gaps. Thereby, the optical fiber 1 a can bemore reliably protected from external force.

It should be noted that the technical scope of the present invention isnot limited to the above-described embodiments, and variousmodifications can be made without departing from the spirit of thepresent invention.

For example, although the interposed layer 4 in the above-describedembodiments has a single-layer structure, the interposed layer 4 mayhave a multi-layer structure as shown in FIG. 6. The multi-layerstructure is a structure including a first layer element 4 a formed fromthe sheet material 3 that is in contact with the core 8 and a secondlayer element 4 b formed from the sheet material 3 located radiallyoutside the first layer element 4 a. As described above, by adopting aconfiguration in which the sheet materials 3 are double overlapped inthe radial direction, the optical fiber 1 a can be more reliablyprotected from external force.

The sheet material 3 included in the first layer element 4 a and thesheet material 3 included in the second layer element 4 b may includedifferent types of fibers 3 a. In this case, compared to the case wherethe same type of fiber 3 a is used for the first layer element 4 a andthe second layer element 4 b, the disadvantage of each fiber 3 a can becompensated for while making use of the advantage of each fiber 3 a.

Further, one of the first layer element 4 a or the second layer element4 b may be a single sheet material 3 which is wound around the core 8into a cylindrical shape. In the example of FIG. 6, the first layerelement 4 a is configured by a plurality of sheet materials 3, and thesecond layer element 4 b is configured by one cylindrical sheet material3. When one sheet material 3 is formed in a cylindrical shape, the sheetmaterial 3 may be spirally wound around the core 8. Alternatively, thesheet material 3 may be simply wrapped from the outside of the core 8 inthe radial direction such that the sheet material 3 has a C-shape withan opening closed. In these cases, in addition to the layer elementhaving the plurality of sheet materials 3, the core 8 is further wrappedby one cylindrical sheet material without any gaps, so that the opticalfiber 1 a can be more reliably protected from external force.

Further, in the above-described embodiments, the plurality of sheetmaterials 3 extend linearly along the longitudinal direction, butwithout being limited thereto, the plurality of sheet materials 3 may bewound around the core 8 spirally or in an SZ shape along thelongitudinal direction.

In a case where the sheet material 3 extends linearly, when the opticalfiber cables 10A to 10D are bent, elongation strain is concentrated on aspecific sheet material 3 located outside the bend. On the other hand,in a case where the sheet material 3 is spirally wound, when the opticalfiber cables 10A to 10D are bent, compressive strain is applied insidethe bend and elongation strain is applied outside the bend, to eachsheet material 3. Due to this difference, the maximum value of theelongation strain applied to each sheet material 3 is smaller when thesheet material 3 is spirally wound than when the sheet material 3extends linearly. As a result, by spirally winding the sheet material 3,the optical fiber cables 10A to 10D can be easily bent.

On the other hand, in a case where the sheet material 3 is woundspirally, the core 8 may be tightened by the sheet material 3 when theoptical fiber cables 10A to 10D are pulled in the longitudinaldirection. On the other hand, in a case where the sheet material 3 iswound in an SZ shape, tightening of the core 8 by the sheet material 3can be suppressed.

However, when the sheet material 3 extends linearly, it is consideredthat the optical fiber cables 10A to 10D can be easily manufactured thanwhen the sheet material 3 is wound spirally or in an SZ shape.

Whether to make the sheet material 3 linear, wound spirally or wound inan SZ shape may be appropriately selected according to the performancerequired for the optical fiber cables 10A to 10D.

Further, the ripcord 7 may be formed of a fiber reinforced plastic,which is the same material as the sheet material 3, in a rod shape.

Further, the sheet material 3 may be used as a ripcord for tearing thesheath 5 along the longitudinal direction. Since the sheet material 3has a high tensile strength and does not break unintentionally whenpulled, the sheath 5 can be reliably torn. When the sheet material 3 isused as a ripcord, the optical fiber cable may not include the ripcord7.

In addition, the optical fiber cable of the above-described embodimentsmay not have a configuration such as a holding binder for fixing thearrangement of the plurality of sheet materials 3. Therefore, it can bemanufactured more easily than an optical fiber cable in the related art.

Further, in the optical fiber cable 10D (FIG. 5A) of one or moreembodiments, the adhesive 6 covers the entire outer peripheral surfaceof the interposed layer 4. However, as shown in FIG. 7, the adhesive 6may be provided intermittently in the circumferential direction on theouter peripheral surface of the interposed layer 4 so as to cover theboundary between the sheet materials 3, for example. In this case, theadhesive 6 may be applied intermittently in the circumferentialdirection to the outer peripheral surface of the interposed layer 4 soas to cover only the boundary portion between the sheet materials 3, andthe adhesive 6 may be cured. Alternatively, the matrix 3 b itself may beused as the adhesive 6 by heating only the boundary portion between thesheet materials 3 to melt the matrix 3 b in that portion and curing thematrix 3 b again.

In addition, without departing from the spirit of the present invention,it is possible to appropriately replace the constituent elements in theabove-described embodiment with well-known constituent elements, and theabove-described embodiment and modification examples may beappropriately combined.

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims.

REFERENCE SIGNS LIST

10A, 10B, 10C, 10D Optical fiber cable

1 a Optical fiber

3 sheet material

3 a fiber

3 b matrix

4 interposed layer

4 a first layer element

4 b second layer element

5 sheath

7 ripcord

8 core

1. An optical fiber cable comprising: a core that includes opticalfibers; a sheath that accommodates the core; an interposed layerdisposed between the core and the sheath; and a ripcord disposed betweenthe interposed layer and the sheath, wherein the interposed layerincludes sheet materials arranged in a circumferential direction of theoptical fiber cable to cover the core, each of the sheet materialsincludes fibers solidified by a matrix, and the ripcord is disposedradially outside the sheet material, and at least a part of the ripcordis embedded in the sheath.
 2. The optical fiber cable according to claim1, wherein the interposed layer has a single-layer structure, and eachof the sheet materials is at least partially in contact with the core.3. The optical fiber cable according to claim 1, wherein in at least apart of adjacent ones of the sheet materials, end parts of the adjacentsheet materials in the circumferential direction abut each other.
 4. Theoptical fiber cable according to claim 1, wherein the interposed layerhas a multi-layer structure including at least a first layer element anda second layer element that are formed from the sheet materials, thefirst layer element is in contact with the core, and the second layerelement is disposed outside the first layer element.
 5. The opticalfiber cable according to claim 4, wherein the first layer element andthe second layer element include different types of fibers.
 6. Theoptical fiber cable according to claim 1, wherein the ripcord is fixedto at least one of the sheet materials.
 7. The optical fiber cableaccording to claim 1, wherein the sheet materials are fixed to thesheath by permeating a part of the sheet materials with a constituentmaterial of the sheath.
 8. The optical fiber cable according to claim 1,wherein the sheet materials are fixed to each other.
 9. The opticalfiber cable according to claim 1, wherein the sheet materials extendlinearly along a longitudinal direction of the optical fiber cable. 10.The optical fiber cable according to claim 1, wherein the adjacent sheetmaterials in the circumferential direction are in contact with eachother, such that the core is covered with the sheet materials withoutgaps, and the sheet materials are disposed over the entire circumferenceof the core in cross-sectional view.
 11. The optical fiber cableaccording to claim 1, wherein the core does not include a wrapping tubethat wraps the optical fibers, and the interposed layer is in contactwith the optical fibers.